The objective of this rsearch plan is to investigate the mechanism by which neuropeptides regulate hormone secretion and synthesis by target cells. The studies will utilize two clonal cell lines derived from anterior pituitary tissue and one clonal cell line derived from the endocrine pancreas. These cell lines have retained many of the differentiated functions of the gland of origin and possess several unique properties which readily permit studies that would be difficult or impossible to perform in other systems. Aspects of the mechanism of action of two neuropeptides will be examined: somatostatin and bombesin. Five specific areas will be investigated. 1. The regulation of hormone secretion and synthesis by target cells will be characterized for each peptide. The validity of the cell lines as model systems will be tested by comparing the biological responses of each of the cell strains with the response of the target gland In Vivo and in primary culture; 2. Specific receptors for each peptide will be characterized both by binding studies with radiolabeled peptide analogs and biochemically. 3. The regulation of receptors by homologous and heterologous ligands will be examined and related to changes in target cell responsiveness; 4. The internalization and processing in receptor regulation; 5. The role of cyclic nucleotides and protein phosphorylation in the mechanism by which these neuropeptides regulate hormone secretion will be determined. The methodology will involve primarily biochemical and immunological procedures. These studies will provide progress towards the long-term objectives of this laboratory: namely understanding, at a molecular level, the biochemical steps involved in the action of neuropeptides on endocrine glands from the initial interaction with target cell receptors to the final cellular response.